Composition and Development Prospects of Scented Rice

, , , ,

Tropical Crops Genetic Resources Institute of Chinese Academy of Tropical Agricultural Sciences, Danzhou 571737, China

CompositionandDevelopmentProspectsofScentedRice

JiankaiSHEN*,ZhenyuXIE,ZhizhouHE,QiyunLIN,MingYIN

Tropical Crops Genetic Resources Institute of Chinese Academy of Tropical Agricultural Sciences, Danzhou 571737, China

Containing higher aromatic composition, scented rice is better than ordinary rice varieties in taste and nutrition. Major composition of scented rice is 2-acetyl-1-pyrroline (2-AP). Different scented rice varieties have different content of 2-AP. The content of 2-AP is not only influenced by genetic factors, but also closely connected with types and content of nutrition elements in soil, soil moisture management, environmental temperature, and storage. 2-AP synthesis and regulation are possibly connected with Proline and enzyme.

Scented rice, 2-acetyl-1-pyrroline (2-AP), Scented substance, Proline

1 Introduction

Scented rice is the rice with natural chemical compounds which give it a distinctive scent. It can be used just like conventional rice for cooking, but adds a new dimension of flavor and aroma to meals[1]. Apart from special natural fragrance, scented rice also has high nutritional value, and contains many kinds of amino acids, proteins, alkaloids, vitamin B1, and vitamin B2, and other essential nutrients for human[2]. Sekharetal[3]measured composition of amino acids in 12 varieties of scented rice (including Basmati 370) and ordinary rice, and found that average total amino acids in 12 varieties of scented rice is 77.13 mg/g, the protein is 14.03% higher than ordinary rice, and the average content of granular protein in 12 varieties of scented rice is 11.22-11.36%, higher than the control group. Scented rice contains high protein and amino acids. According to reports, Henan Yangguang scented rice is rich in trace elements such as Se, Zn and Ca, and many kinds of vitamins, and many essential amino acids beneficial to human health. Scented rice features excellent taste, is nutritious and healthy, and has high economic value, so it is highly favored by consumers and becomes a hot spot of current rice researches[5]. In recent years, China has undertaken extensive researches about scented rice, explored a good many local scented rice varieties, and selected a lot of new scented rice varieties. Content of scented substances in scented rice is not only regulated by genetic substance, but also influenced by cultivation environment and methods[5]. Strengthening research on breeding and cultivation of new varieties of scented rice can promote production and development of scented rice in China and diversified development of scented rice in China, and enhance international competitiveness of China’s scented rice.

2 Varieties of scented rice

Thailand has cultivated many varieties of scented rice, such as Jasmine; Pakistan has Basmati rice; Australia has Goolarah and YRF varieties; the United States has developed Jasmine rice[6]. With more than 100 rice production countries, China is the kingdom of rice, and the rice yield accounts for 35% of world rice yield ranking the first place in the world[7]. Planting of scented rice has a long history in China and it can be dated back to more than 1800 years ago[8]. China is vast in territory, great difference in geographical environment, climatic conditions, forming rich germplasm resources and precious local varieties of accented rice, such as Jiangyong scented rice of Hunan Province, Qubu scented rice of Shandong Province, and Jingxi scented rice of Beijing[9]. Through seed introduction and using local scented rice varieties, China has cultivated Zhongjian 2, Yixiang 1577, and a good many new scented rice varieties[10-13].

China has taken fragrance of rice as an essential quality indicator[14]. Generally, scented rice can be divided into Pandanus tectorius scented rice, violet scented rice, Jasmine scented rice, lettuce scented rice, hickory nut scented rice, Basmati scented rice, toasted bread scented rice, crispy rice scented rice, popcorn scented rice; major volatile substances include hydrocarbons, aromatic hydrocarbons, aldehydes, ketones, esters, acids, alcohols, and alcohol-based alkylene, heterocyclic compounds,etc[15].

3 Composition and approach of fragrance of scented rice

Yajimaetal[16-17]measured composition of Japanese scented rice Oshihikari and Kaorimai using Gas Chromatograph Mass Spectrometer and found 114 substances in those scented rice varieties, compared with ordinary rice varieties, pyrrolidinone and indole are significantly higher. Butteryetal[18]found that the content of 2-acetyl-1-pyrroline (2-AP) in Basmati 370, Khao Dawk Mali, Malagkit Sungsong, and Hieri is several to several dozens of times of ordinary rice. Danielsetal[19]also found that 2-AP is the major composition of scented rice, 2-AP concentration in brown rice is 1500 μg/kg, higher than findings of Butteryetal.[20]; the closer to seed coat, the higher the content. Mahattanataweeetal[21]found 26, 23, 22 kinds of scented substances in Jasmine, Basmati, and Jasmati scented rice respectively; 2-AP exists in those three types of scented rice varieties; 2-acetyl-2-thiazoline (2-AT) only exists in Jasmine scented rice; they found dimethyl sulfide, 3-Methyl-2-butene-1-thiol, 2-Methyl-3-Furanethiol, dimethyl trisulfide, and 3-Methylthio propionaldehyde also are scent active substances. Bryantetal[22]believed that volatile substances of rice are diversified. 93 types of volatile substances were found in rice. Except 2-AP, there are differences in volatile substances of scented rice and ordinary rice; 16 types of volatile substances exist in scented rice, and some are unique to scented rice[23]. Gu Jianmingetal[24]analyzed composition of fragrant japonica rice 8618 using, found that No.6 peak is consistent with mass fragmentography of artificially synthetic 2-AP GC-MS, and its fragrance has popcorn taste like artificially synthetic 2-AP. Besides, they also analyzed possible lytic pathways of 2-AP under mass spectral lytic theory[25]. Pinson[26]studied scented substances of scented rice Della-xa, A-301, Jasmine 85, and Amber, and concluded that the difference between scented rice and ordinary rice lies not in existence of 2-AP, but in the content of 2-AP. Yu Biyuetal[27]also found 2-AP in Baixiangnuo (a common vegetable corn variety). Mathureetal[28]found that 2-AP content of non Basmati scented rice is higher than Basmati; 2-AP content is positively correlated with 1-tetradecene and indole, negatively correlated with benzyl alcohol; content of nonanal, caprylic aldehyde base, aldehyde, and 1-Octen-3-ol is different between Basmati and ordinary rice varieties. These indicate that fragrant substances of scented rice are diversified, deep or light scent of scented rice may be related with combined action of many scented substances; major element of scent is 2-AP; indole, phenylethanol, a-pyridine is higher in scented rice than ordinary rice varieties[29]. With constant progress in technologies, new fragrant substances in scented rice are gradually recognized.

According to mass researches, 2-AP nitrogen source precursor is proline[18, 30-31], through a series of enzymatic action of proline oxidase, proline is finally converted to 2-AP[32]. Gu Jianmingetal[24]found that low soluble molecular weight extract of corn contains much free L-proline, glucose, and fructose, and heating L-proline and glucose and fructose can generate 2-AP, proved L-proline and glucose and fructose are precursors of 2-AP, and derived the approach of generation of 2-AP through heating, but did not explain all intermediates in the whole reaction process. Chenetal[33]held that betaine aldehyde dehydrogenase (BADH2) catalyzes betaine aldehyde in cytoplasm, and γ-Aminobutyraldehyde oxidation reaction with 3-amino-propionaldehyde, while GABald may be probably precursor of 2-AP biosynthesis. Tadashietal[34]proved that the most important precursor for generation of 2-AP in rice seedlings is proline, proline forms pyrroline-5-carboxylate through catalysis of proline oxidase, forms pyrroline through catalysis of pyrroline-5-carboxylate decarboxylase, and finally forms 2-AP through transferase action of pyrroline and acetyl-CoA. Free proline, proline oxidase, and total free amino acid are major factors for synthesis of aroma of scented rice, while there is no significant correlation between ornithine transaminase and aroma of scented rice[35]. The synthesis of scented substances is related to proline and prolinase, but it is still not clear about dynamic matters in 2-AP and the key enzyme influencing generation of 2-AP in grains.

4 Factors influencing quality of fragrance of scented rice

4.1NutritionelementsAroma of scented rice is not only influenced by genetic matters of scented rice, but also influenced by growth environment and nutritional ecology. Huang Shuzhen[36-37]found that quality of scented rice in scented rice production area is better than other areas; organic matters, total nitrogen, available nitrogen, total phosphorus, available phosphorus, Fe, Mn, Cu, and Zn of soil in scented rice production area is higher than non-production areas; lanthanum (la), titanium (ti), and cobalt (Co) in soil and rice stems and leaves and vanadium and nickel in soil are higher than non-production areas, and lanthanum and titanium may be essential elements influencing the generation of aroma of scented rice. Sun Shuxiaetal[38]also proved that planting scented rice in soil containing higher total nitrogen, available nitrogen, and Zn, the aroma of scented rice will be denser. Yangetal[39]studied factors influencing generation of aroma of scented rice varieties in China, and found that the higher the total nitrogen in soil, the denser the aroma of scented rice, so the total nitrogen increase is the major factor influencing increase of aroma. Increasing nitrogen fertilizer can increase content of free proline, so as to increase 2-AP content in scented rice, but there are differences between different scented rice varieties[40]. Lanthanum fertilizer (lanthanum chloride) application can increase yield and aroma of scented rice, the highest application of lanthanum fertilizer (LaCl3) for the highest content of aroma in brown rice is 3180 mg/kg, the content of LaCl3for increasing yield and aroma of scented rice is 100 mg/kg[41], lanthanum fertilizer can improve activity of proline oxidase, so as to reduce proline content of rice grain[42]. Zn fertilizer can significantly increase 2-AP content in rice grain of different scented rice varieties, but the amount of increase is different for different varieties[43], and the optimum ZnCl2base fertilizer application for increasing aroma concentration of scented rice is 80-120 mg/kg[44]. Potash fertilizer can increase yield of scented rice and aroma of brown rice, and plays a certain role in improving quality of scented rice[45]. Application of potash fertilizer can significantly increase free proline and improve proline dehydrogenase activity, increase 2-AP content of scented rice about 10.70-67.65%, there is certain difference between aroma increase and application of potash fertilizer, and through quadratic curve fitting, the highest potash fertilizer application for aroma of scented rice is K2O123.46-187.50kg/hm2[46]. Therefore, appropriate application of plant nutrients can result in changes in precursor proline and related enzyme activities for generation of 2-AP, so as to bring about changes in aroma of scented rice[47-48]. This is the most simple and effective method for adjusting aroma of scented rice in cultivation of scented rice varieties.

4.2MoistureResearches indicate that proper irrigation can effectively increase aromatic composition of scented rice without influencing physiological features of rice growth, and also can increase aroma of scented rice[49]. When moisture is kept in 0-(-25±5) kPa at the tillering stage, it can significantly increase aromatic components of scented rice and free proline in rice grain, and also can improve proline oxidase in leaves, stem and sheath and rice grain in mature period; when the moisture is kept in 0-(-50±5) kPa at the tillering stage, the aromatic components of scented rice drops[50]; if the moisture is kept 0-(-25±5) kPa at booting stage, it can increase aromatic components of scented rice, improve proline oxidase activity in leaves and rice grain, while it will reduce aromatic components of scented rice when soil moisture is in 0-50 (±5) kPa[51]. Certain water and nitrogen interaction can increase 2-AP content of scented rice, moisture stress and suitable tillering cultivation condition can realize higher level of aromatic components[52]. These indicate that proper management of soil moisture is an essential measure for adjusting aroma of scented rice.

4.3TemperatureEnvironmental temperature not only influences rice quality, but also affects its aroma. Generally speaking, aroma of scented rice mature in high temperature condition will be weak, while aroma of scented rice mature in lower temperature will be denser[53]. Average daily temperature of 30℃ will reduce seed setting, filled grains, head rice rate, amylose content, alkali spreading value, flavor score and aroma. In grain-filling period, average daily temperature of 23℃ can realize higher yield, quality and aromatic components[54]. Yang Shuyingetal[55]found that during early and middle grain filling period, the scented rice varieties have denser aroma with low average-daily-temperature,low highest-daily temperature, low lowest-daily-temperature. Aromatic components are varied. Low average daily temperature and great daily temperature difference can increase free amino acids and unsaturated aliphatic acids of rice, thus it may be one of reasons for dense aroma of Chinese local scented rice varieties. Average daily temperature and relative humidity in grain filling period are major factors influencing content of soluble proteins of rice grain, and there are differences in soluble proteins of rice grain between different scented rice varieties[56]. Through experiment, Yang Xiaojuanetal[57]found that early season rice sowed in March 10 in south China contains high 2-AP, and 2-AP is negatively correlated with illumination hours. For the sown period with high 2-AP content, the free proline and proline dehydrogenase activity keep higher level. Late rice (sowed in July 20) contains higher 2-AP; for the sown period with high 2-AP content, the free proline and proline dehydrogenase activity keep higher level[58]. Thus, temperature is an essential factor influencing rice quality, and its major approach may be activity of proline and proline enzyme. Selecting suitable sowing time is an important measure for improving quality of scented rice.

4.4IlluminationYang Xiaojuanetal[57]found that scented rice with higher content of 2-AP contains high free proline and activity of proline dehydrogenase, and 2-AP is negatively correlated with illumination time. Mo Zhaowenetal[59]found shading 15 days after flowering, the content of 2-AP in rice grain also significantly increases, and it also can increase content of GABA (γ-aminobutyricacid). In other words, weak light can increase aromatic content of scented rice.

4.5OtherfactorsApart from the above factors, changes in aromatic components of scented rice are also influenced by other factors. Extracting natural aroma to store rice can increase content of 2-AP[61]. Gayetal[62]held that salt of soil plays a positive role in 2-AP of scented rice, but salt stress will influence yield of scented rice. Besides, grain weight and soil electric conductivity are negatively correlated with 2-AP content. They believed that increase of 2-AP in scented rice is resulted from shrinkage of grain size due to salt. However, Fitzgeraldetal[63]studied the relation between leaves of scented rice and 2-AP content and salt stress in Jasmine and Basmati, and found that there is no significant stress relation between them. Study of Sugunyaetal[53]indicated that lower temperature for desiccation grain can promote increase of 2-AP; during 10 months storage period, with increase of storage time, the content of 2-AP drops.

5 Application prospects

Unique aroma and nutrition of scented rice make it ranking in an important position in international rice trade. According to statistics of Food and Agriculture Organization of the United Nations, rice consumption has reached 407.8 million tons in 2000, and the trade reached 17.116 million tons[6]. The price of scented rice in international market is 2-3 times or even 10 times higher than conventional rice, showing huge commercial value and market potential, and increasingly favored in recent years. Besides, developing scented rice has higher economic benefits compared with conventi onal rice varieties. Scented rice has higher economic benefits, so it may be an effective approach for increasing income of farmers in mountainous areas. At present, domestic scented rice has price up to 3-4 times of the ordinary rice, and 2 times higher than conventi onal high quality rice[64]. Apart from food, scented rice can also be used as special purpose for industrial development, such as making rice beer, rice wine, rice vinegar, and rice cake. Therefore, application of scented rice is large and development prospect of scented rice industry is promising. In recent years, demand of scented rice gradually rises in all over the world. China is the largest rice production country, and scented rice varieties are varied, but the export is nearly zero. Further speeding up research and development of scented rice varieties and cultivation technologies are of great significance for development of China’s scented rice industry and effective supplement of demands of scented rice market.

[1] Ministry of Agriculture of the People’s Republic of China. The industrial standard of Ministry of Agriculture of the People’s Republic of China，aromatic rice NY/T 596-2002[S]. (in Chinese).

[2] YU GL. The genetic characteristics and nutritional quality of fragrant rice[J]. Journal of Zhejiang Agricultural Sciences， 1987(3)： 113-115.(in Chinese).

[3] Sekhar BPS, Reddy GM. Amino acid profiles in some scented rice varieties[J]. Theoretical and Applied Genetics, 1982, 62(1): 35-37.

[4] ZHANG ZW, WANG J, TANG YQ,etal. Aroma genetic breeding and its cultivation of aromatic rice[J].Genomics and Applied Biology， 2010, 29 (3)：550-555.(in Chinese).

[5] CUI GY. Review of the volatile component of rice[J]. Food Science，1995, 16(9)：7-9.(in Chinese).

[6] XIE LH, DUAN BW, SUN CX. The sources, fragrance and inheritance of aromatic rice[J]. World Agriculture， 2003(11)： 49-50.(in Chinese).

[7] HE ZW. Present condition, problem, countermeasure on the development of Chinese rice industry[J]. Journal of Agrotechnical Economics， 2003(6)： 41-44.(in Chinese).

[8] LI LF, LI J. The germplasm of aromatic rice and its research progress[J]. Journal of Shanghai Agricultural College， 1997, 15(4)： 305-309.(in Chinese).

[9] ZI YZ. Chatacteristics of scent type rice & its improvement[J]. Journal of Xichang College， 2004， 18(1)： 69-72.(in Chinese).

[10] ZHAO ZH, ZHANG SH, ZHOU B,etal. A new fragrant rice-Xiangwanxian 10[J]. China Seed Industry， 2004(6)： 54-58.(in Chinese).

[11] WANG JL. A new high-quality rice Zhongjian 2[J]. China Rice，2003(4)：19.(in Chinese).

[12] CHEN YX, XU KC. Developing Yi acronym serial seed industry based on the advantages of aromatic rice[J]. China Seed Industry， 2005(3)： 31-33.(in Chinese).

[13] GUO SP. Comparison test of premium quality flavor rice varieties[J]. Seed World, 2005(4): 26-27.(in Chinese).

[14] YOU QR, HUANG TX, ZHOU SQ,etal. Study on heredity and utilization of fragrance for a rice variety A04[J]. Fujian Science and Technology of Rice and Wheat, 2003, 21(4): 21-23.(in Chinese).

[15] LV YM, TAN WP, XIAO CL. Summarization of the scent of scented rice[J]. Hunan Agricultural Sciences， 2010(11)： 19-20， 23.(in Chinese).

[16] Yajima I, Yanai T, Nakamura M,etal. Volatile flavor components of cooked rice Kaorimai[J]. Journal of the Agricultural and Food Chemistry, 1979(43): 2425-2429.

[17] Yajima I, Yanai T, Nakamura M,etal. Volatile flavor components of cooked rice[J]. Journal ofthe Agcultural and Food Chemistry, 1978 (42): 1229-1 233.

[18] Buttery RG, Ling LC, Juliano BO,etal. Cooked rice aroma and 2-acetyl-1-pyrroline[J]. Journal of the Agricultural and Food Chemistry, 1983,31(4): 823-826.

[19] Daniels MJ, Marks BP, Siebenmorgen TJ,etal. Effects of long-grain rough rice storage history on end-use quality[J]. Journal of Food Science, 1998,63(5): 832-840.

[20] Buttery RG, Juliano BO, Ling LC. Identification of rice aroma compound 2-acetyl-1-pyrroline in pandan leaves[J]. Chemistry & Industry,1983(12): 478-478.

[21] Mahattanatawee K, Rouseff RL. Comparison of aroma active and sulfur volatiles in three fragrant rice cultivars using GC-Olfactometry and GC-PFPD[J]. Food Chemistry, 2014(154): 1-6.

[22] Bryant RJ, McClung AM. Volatile profiles of aromatic and non-aromatic rice cultivars using SPME/GC-MS[J]. Food Chemistry, 2011,124 (2): 501-513.

[23] Sung J, Kim BK, Kim BS,etal. Mass spectrometry-based electric nose system for assessing rice quality during storage at different temperatures[J]. Journal of Stored Products Research, 2014(59): 204-208.

[24] GU JM, XU XH. Present and prospects for research on "scented rice"-like aroma compounds: A review[J]. Journal of Shanghai University(Natural Science)， 2002 , 8(3)：227-231. (in Chinese).

[25] LI Y. The protective measures of Thailand to the quality of fragrant rice[J]. World Tropical Agriculture Information， 2005(1)： 28.(in Chinese).

[26] Pinson S R M. Inheritance of aroma in six rice cultivars[J]. Crop Science, 1994, 34 (5) ：1151-1157.

[27] YU BY, LIU XN, WANG J. Study on chemical constitution of BaiXiangnuo eice by gas chromactography-mass spectrometry[J]. Chinese Journal of Spectroscopy Laboratory， 2000， 17 (6)： 538-642.(in Chinese).

[28] Mathure SV, Jawali N, Thengane RJ,etal. Comparative quantitative analysis of headspace volatiles and their association with BADH2 marker in non-basmati scented, basmati and non-scented rice (Oryza sativa L.) cultivars of India[J]. Food Chemistry, 2014(142)： 383-391.

[29]ZHU KY, GONG CR, ZHU GQ,etal. Cultural techniques of quality scented rice variety "Xiangwanxian 13"[J]. Hunan Agricultural Sciences， 2002(4)：31-32.(in Chinese).

[30] Romanczyk L J, McClelland C A, Post L S,etal.Formation of 2-acetyl-1-pyrroline by several Bacillus cereus strains isolated from cocoa fermentation boxes[J]. Journal of Agricultural and Food Chemistry, 1995, 43(2)： 469-475.

[31] Thimmaraju R, Bhagyalakshmi N, Narayan M S,etal. In vitro culture of Pandanus amaryllifolius and enhancement of 2-acetyl-1-pyrroline, the major flavouring compound of aromatic rice, by precursor feeding of L-proline[J]. Journal of the Science of Food and Agriculture, 2005, 85(15)：2527-2534.

[32] Giovanni M Cordeiro, Mandy J Christopher, Robert J Henry,etal. Identification of microsatellite markers for fragrance in rice by analysis of the rice genome sequence[J]. Molecular Breeding,2002,9(4): 245-250.

[33] CHEN S, YANG Y, SHIW,etal. Badh2, encoding betaine aldehyde dehydrogenase, inhibits the biosynthesis of 2-acetyl-1-pyrroline, a major component in rice fragrance[J]. Plant Cell, 2008, 20(7): 1850-1861.

[34] Yoshihashi T, Huong NTT, Inatomi H. Precursors of 2-acetyl-1-pyrroline, a potent flavor compound of an aromatic rice Variety[J]. Journal of Agricultural and Food Chemistry, 2002, 50 (7): 2001-2004.

[35] DUAN MY, LI GX, TIAN H,etal. Primary research on the physiological characteristics of aroma formation in aromatic rice[J]. Journal of Hunan Agricultural University，2009, 35(1): 5-8.(in Chinese).

[36] HUANG SZ. The relationship between soil properties of fragrant rice producing area in Hu’nan and rice quality[J]. Hunan Agricultural Sciences， 1990(4):37-40.(in Chinese).

[37] ZHENG CG. Influence of micro elements on scented rices yield and quality[J]. Journal of Shihezi University(Natural Science)， 2005, 23(4):70-72.(in Chinese).

[38] SUN SX, LIU SC. Study on the fragrance of rice and the effect of N and Zn on the fragrance[J].Acta Agronomica Sinica， 1991,17(6): 430-435.(in Chinese).

[39] YANG S, ZOU Y, LIANG Y,etal. Role of soil total nitrogen in aroma synthesis of traditional regional aromatic rice in China[J]. Field Crops Research, 2012(125): 151-160.

[40] ZHONG Q, TANG XR. Effects of nitrogen application on aroma of aromatic rice and their mechanism[J]. Guangdong Agricultural Sciences， 2014, 41(4)： 85-87.(in Chinese).

[41]XIAO D, HUANG JX, DUAN MY,etal. Effects of different applications of LaCl3on yield and aroma contents of aromatic rice[J]. Journal of South China Agricultural University， 2010(1)： 115-116.(in Chinese).

[42] XIAO D, HUANG JX, TANG XR,etal. Effect of LaCl3 on aroma contents in brown rice of aromatic rice and its mechanism[J]. Southwest China Journal of Agricultural Sciences， 2009, 22(2)：364-367.(in Chinese).

[43] HUANG JX, XIAO D, TANG XR. Effect of zinc on the yield, aroma and quality of aromatic rice[J]. Tillage and Cultivation， 2010(3)： 5-7.(in Chinese).

[44] HUANG JX, XIAO D, DUAN MY,etal. Effects of different applications of ZnCl2on the yield and aroma content of aromatic rice[J]. Acta Agriculturae Boreali-Sinica，2008, 23(B10)： 290-292.(in Chinese).

[45] LUO YM, TANG XR, PAN SG,etal. Changes of yield and photosynthetic production of aromatic rice in response to potassium application[J]. Jiangsu Journal of Agricultural Sciences， 2014(2)：237-242.(in Chinese).

[46] LUO YM, XIAO LZ, PAN SG,etal. Effects of potassium fertilizer on aroma and quality of aromatic rice[J]. Southwest China Journal of Agricultural Sciences， 2014, 27 (3)： 1147-1153.(in Chinese).

[47] HUANG ZL, TANG XR, WANG YL,etal. Effects of increasing aroma cultivation on aroma and grain yield of aromatic rice and their mechanism[J]. Scientia Agricultura Sinica，2012, 45(6)：1054-1065.(in Chinese).

[48] TANG XR, WU M. Effects of application of zinc, iron and lanthanum on contents of aroma in brown rice and proline in flag leaf of aromatic rice[J]. Hybrid Rice, 2006, 21(6)：69-72. (in Chinese).

[49] TIAN K, TANG XR, DUAN MY,etal. Effects of irrigation on aroma content and physiological characteristics of aromatic rice at grain filling stage[J]. Journal of Irrigation and Drainage， 2010, 29(6)： 91-93. (in Chinese).

[50] WANG P, XIAO LZ, TANG XR,etal. Effects of different irrigation modes on aroma content of aromatic rice at tillering stage[J]. Journal of Irrigation and Drainage， 2013, 32(1)：103-105.(in Chinese).

[51] WANG P, TANG XR, TIAN H,etal. Effects of different irrigation modes on aroma content of aromatic rice at booting stage[J]. Guangdong Agricultural Sciences，2013， 40(8)： 1-3. (in Chinese).

[52] LI YH, TANG XR, PAN SG,etal. Effect of water-nitrogen interaction at tillering stage on aroma, grain yield and quality of aromatic rice[J]. Acta Agriculturae Boreali-Sinica，2014 (1)： 159-164. (in Chinese).

[53] Wongpornchai S, Dumri K, Jongkaewwattana S,etal. Effects of drying methods and storage time on the aroma and milling quality of rice (Oryza sativa L.) Khao Dawk Mali 105[J]. Food Chemistry，2004, 87(3): 407-414.

[54] XU ZJ, XIAO LZ, WANG W,etal. Effect of temperature on yield and quality of aromatic rice[J]. Journal of South China Agricultural University， 2006, 27(4): 1-4. (in Chinese).

[55]YANG SY, ZPOU YB, XIA B,etal. Effect of climatic ecological factors of main aromatic rice regions in Hu’nan on aroma quality of rice[J]. China Rice，2013,19(4):44-49. (in Chinese).

[56] DENG M, YANG SY, ZOU YB,etal. Effects of the growth habitat on the content of soluable protein in aromatic rice grains[J]. Acta Botanica Boreali-Occidentalia Sinica， 2011, 31(11)：2276-2282. (in Chinese).

[57] YANG XJ, TANG XR, WEN XC,etal. Effects of sowing date on aroma formation, quality and yield of early season aromatic rice[J]. Acta Agriculturae Boreali-Sinica， 2014(3): 128-135. (in Chinese).

[58] YANG XJ, TANG XR, WEN XC,etal. Effects of sowing date on 2-acetyl-l-pyrroline content and yield of late season aromatic rice[J]. Acta Ecologica Sinica， 2014， 34(5)： 1 156-1 164.(in Chinese).

[59] MO ZW, WANG YL, XIAO F,etal. Effects of 15-day continuously shading treatment after flowering on grain yield, quality and aroma of aromatic rice[J]. Journal of South China Agricultural University, 2015, 36(3): 45-48. (in Chinese).

[60] Mo Z, Li W, Pan S,etal. Shading during the grain filling period increases 2-acetyl-1-pyrroline content in fragrant rice[J]. Rice, 2015, 8(1)： 9.

[61] Laohakunjit N, Kerdchoechuen O. Aroma enrichment and the change during storage of non-aromatic milled rice coated with extracted natural flavor[J]. Food Chemistry, 2007, 101(1): 339-344.

[62] Gay F, Maraval I, Roques S,etal. Effect of salinity on yield and 2-acetyl-1-pyrroline content in the grains of three fragrant rice cultivars(OryzasativaL.) in Camargue (France)[J]. Field Crops Research, 2010,117(1): 154-160.

[63] Fitzgerald TL, Waters DLE, Henry RJ. The effect of salt on betaine aldehyde dehydrogenase transcript levels and 2-acetyl-1-pyrroline concentration in fragrant and non-fragrant rice (Oryza sativa)[J]. Plant Science, 2008, 175(4)：539-546.

[64] S Sarkarung, B Somrith, S Chitrakorn,etal.Thailand’s sweet rice[J]. China Rice, 2003(4)：40-41.(in Chinese).

November 10, 2015 Accepted: December 18, 2015

Supported by Special Fund for Basic Scientific Research Project in Chinese Academy of Tropical Agricultural Sciences (1630032014031); Special Fund for Scientific and Technological Project of Chinese Academy of Tropical Agricultural Science "Research on Selection of High Efficient Varieties of Grain Crops in Hot Region" (0315012).

*Corresponding author. E-mail: shh868@126.com